The objective of the proposed research is to gain information concerning the regulation of cytosolic-mitochondrial interactions in liver under normal and pathological conditions so that the nature of metabolic disorders such as diabetes can be more clearly defined. Focus will be placed on the regulation of amino acid metabolism and ureogenesis and its interactions with the pathways of gluconeogenesis and the citric acid cycle. The physiological significance of factors involved in the regulation of carbamyl phosphate synthesis, glutamate dehydrogenase, and transport of amino acids across the mitochondrial membrane will be investigated using both isolated liver mitochondria and isolated rat liver cells. Techniques will be developed for the rapid separation of mitochondria from liver cells incubated under defined conditions without disturbing the contents of metabolites in the cytosolic and mitochondrial compartments. The aim of these studies will be to define the influence of altered substrate and ammonia concentrations, and changes of pyridine nucleotide redox state and energy state in the separate cell compartments on flux through glutamate dehydrogenase, the glutamate translocator and the glutamate:aspartate translocator in relation to urea production from ammonia and added amino acids. By these means, the function and regulation of mitochondria in the intact cell will be assessed directly in relation to external influences affecting whole cell metabolism. Further studies will be directed towards answering the question whether and to what degree altered function of the anion translocators in the mitochondrial membrane account for altered hepatic metabolic functions of the liver induced by imbalances in the plasma levels of insulin, glucagon, corticosteroids and pituitary hormones. A greater understanding of cytosolic-mitochondrial interactions in the cell, which are recognized as obligatory steps of all the major biosynthetic pathways of liver, may lead to new methods of drug therapy for the treatment of metabolic disorders. BIBLIOGRAPHIC REFERENCES: Williamson, John R. and Tischler, Marc Nicotinamide Adenine Dinucleotide Phosphate Redox Potentials in Cytosol and Mitochondria of Rat Liver Cells. Abstract in Fed. Proceedings, in press (1977). Viale, R., Coll, K., Murphy, E., Williamson J.R. Kinetic Mechanism of the Glutamate-Aspartate Translocator. Abstract, Biophysical Society, in press, 1977.